Dynamic positioning (DP) is a method of maintaining the position and heading of a vessel generally by means of the propulsion means of the vessel. Vessels which utilize dynamic positioning include semi-submersible rigs and drillships.
Safety related rules have been set for dynamic positioning ships. These rules define classes DP1, DP2 and DP3. Class rules for DP2 and DP3 vessels demand that position must be maintained following a single fault. In practice this means that blackouts must never be allowed to occur. To achieve this, DP vessels are normally run in a split bus configuration with open busties. For semi-submersible rigs this generally means a two-split configuration, while for drillships a three-split configuration is typical. These configurations are sufficient to prevent blackout and meet the class requirements for DP2 and DP3 operation under most environmental conditions.
Rigs are often operated with extra redundancy in addition to that provided by the split bus configuration. Some rig operators provide rigs with at least two running generators in each split during DP operations, to minimize the risk of partial blackout within each split. However, configurations with several running generators have several drawbacks.